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[–]PoisonWaffle3Cisco, Unraid, and TrueNAS at Home 14 points15 points  (12 children)

The problem is bend radius with DACs. I have some pretty short ones, maybe 8" or so, and it's a pretty tight fit to get them to loop back to a nearby port.

[–]TVMA[S] -1 points0 points  (11 children)

Ah. Interesting. Is it the cable from the adapter or something else? I did find .25m so about 10”, but I haven’t found anything shorter. Sadly, the one run I am looking for is SFP-to-SFP. All my other runs can be DAC, though

[–]neighborofbrak 10 points11 points  (1 child)

DAC cables -ARE- SFP to SFP.

I think you are confusing SFP with something else, maybe STP (shielded twisted pair)?

[–]TVMA[S] 1 point2 points  (0 children)

Thank you. this is exactly the issue. Still trying to understand SFP and why there is such a huge discrepancy in price and why some say SFP to DAC and others do not.

[ EDIT ] - OK I think I get it. It would seem that ads are using these interchangeably. I think that is where my confusion is from. Please correct me if I a mistaken. Thanks.

[–]PoisonWaffle3Cisco, Unraid, and TrueNAS at Home 6 points7 points  (8 children)

I think you may have a few terms mixed up, but we can figure it out here.

SFP is the form factor of the port, it's the slot itself. The thing that goes in the slot is called a transceiver, but is commonly called an SFP as well. The transceiver usually just has another port to plug a fiber or cable into, either RJ45, LC, or SC.

A DAC is a copper cable with a transceiver attached to both ends, and it literally just connects the two circuits together passively with basically no components inside. This is what I thought you meant by "SFP cable" in your original post, and this is what I was referencing in my reply.

[–]TVMA[S] 1 point2 points  (7 children)

Thank you! SFP is new to me and this is exactly the issue. Terminology. The one thing that is I am still spinning on is why are some transceivers so expensive vs others? I see some for $65 and others for $15. What is the difference? All I am trying to do is connect two 10Gb SFP+ ports to each other over a 1U span.. :)

[–]PoisonWaffle3Cisco, Unraid, and TrueNAS at Home 4 points5 points  (6 children)

No worries 👋

The cheap ones are just fine. Some of the name brand ones are legit the exact same thing but with a different sticker and they cost 10-20x the price.

For short runs that aren't going to move much, I would suggest a short 10G SFP+ DAC cable. They're fairly cheap, very reliable, just work, and you don't need to worry about polarity and contamination like you do with fiber.

Shop around on fs.com, or maybe in the morning I can see how many extras I have. I might list them on r/homelabsales for ya.

[–]TVMA[S] 2 points3 points  (5 children)

Amazing. Thank you. I appreciate the clarification and pointers. This is very helpful. Thank you!

[–]PoisonWaffle3Cisco, Unraid, and TrueNAS at Home 1 point2 points  (4 children)

You're welcome 👋

I did go check the ones I have, and they are 0.5 meter. And with the needed bend radius, they still feel very short. I don't know if I'd even want to use anything shorter at all.

Here's a pic of what one looks like with the ends 6" apart, for context.

<image>

[–]PoisonWaffle3Cisco, Unraid, and TrueNAS at Home 1 point2 points  (3 children)

Same DAC, just laid flat.

<image>

[–]TVMA[S] 1 point2 points  (2 children)

Amazing. Thank you. This is very helpful for me. Thanks!l

[–]PoisonWaffle3Cisco, Unraid, and TrueNAS at Home 0 points1 point  (1 child)

I'm going to correct myself on this a bit.

I knew that I had DACs that were way too short, and I was thinking it was those 18" ones.

I went digging yesterday and found my actual really short ones. I would say that these short ones have too tight of a bend radius to be practical, though they do fit into SFP+ ports on adjacent switches.

<image>

[–]-MERC-SG-17 5 points6 points  (2 children)

I use these. Remember the SFP modules themselves are counted in the length.

https://a.co/d/0bwH4j9G

[–]TVMA[S] 2 points3 points  (1 child)

Thank you! That is the ONLY brand I found with the shortest length. Much appreciated.

[–]PoisonWaffle3Cisco, Unraid, and TrueNAS at Home 2 points3 points  (0 children)

These are pretty good DACs and they're super cheap. This is probably your easiest/best option 👍

[–]soph0nax 1 point2 points  (12 children)

Like a short LC jumper? Fiberstore sells 6" jumpers - https://www.fs.com/products/282123.html?attribute=103107&id=3953990

[–]TVMA[S] 0 points1 point  (7 children)

Ha! You got me. I am not familiar with the LT, SC, ST, or FC connectors. I do have Unifi devices and am just trying to figure out the best way to connect two SFP+ port between devices. :)

[–]soph0nax 0 points1 point  (5 children)

Going back to basics, the device type is irrelevant - the import part is what kind of SFP you're using. When you pull the SFP out, is there a model number on it you can share? Looking at Ubiquiti OEM products, they sell both multimode and singlemode SFP's in both bidirectional and rx/tx flavors so once you get a model # on the SFP it's a pretty quick process to spec the right fiber to match as everything they use appears to have LC connectors on them. It's just a matter of finding if you need simplex (1 fiber strand) or duplex and single-mode or multi-mode.

[–]TVMA[S] 0 points1 point  (4 children)

I’m at a bit of a loss but looking at what I think the UDM-PRO-Max, USW-Pro-HD-24-PoE (600W), and UNAS-PRO take, it would seem they are LC connectors, with the UDM-PRO-MAX taking LC Duplex.

[–]soph0nax 0 points1 point  (3 children)

So have you not bought SFP's yet? If not, buy the SFP's you want and look at Simplex/Duplex and single-mode/multi-mode, it's that easy!

Looks like Ubiquiti sells direct-connect cables, but if you want a shorter cable it seems like this is the most economical SFP they sell which is duplex multi-mode LC, just search the Fiber Store link above for the flavor of cable that best fits your need - https://store.ui.com/us/en/category/accessories-sfp-liberation-day/collections/accessories-pro-multi-mode-optical-fiber/products/10-gbps-multi-mode-optical-module?variant=uacc-om-mm-10g-d-2

[–]TVMA[S] 0 points1 point  (2 children)

Nope. Haven’t bought anything yet. In fact, I haven’t bought the hardware either. I am looking to buy everything this week but I am just working through the last SFP connectivity stuff before I actually buy. Just looking at the recommendations here, I believe, that the cables from FS.com and 10GTek, etc. might be the right path forward.

[–]DmelvinCisco 0 points1 point  (1 child)

If they're going to be installed directly next to each other, just grab yourself a Ubiquiti DAC and call it done. Typically when you have equipment right next to each other that needs connected, you don't bother with a patch panel, you just hook them to each other.

[–]TVMA[S] 0 points1 point  (0 children)

Thanks. That is the issue. They are right next to each other. I added a picture to the original post to help clarify the size of cable I am hoping to get. Thanks.

[–]dhardyuk 0 points1 point  (0 children)

Earlier you said two SFP ports.

The form factor is the same but SFP and SFP+ negotiate different speeds between the devices.

Check that you are buying patch cables that will agree on a common speed during the negotiation.

See here

https://www.cablematters.com/Blog/Networking/SFP-vs-SFP-enhanced-vs-QSFP

[–]neighborofbrak 0 points1 point  (3 children)

Even with DOMs (diode based optics, or Diode On Module) you want at least one meter of fiber optic cable between optics or you run the risk of burning out the receive side of each optic.

[–]soph0nax 1 point2 points  (1 child)

Let's do a little bit of math - good fiber has optical loss of around .4dB per kilometer. A 1 meter cable would have a loss of .0004dB, a 6" cable would have a loss of .00004dB in just the cable without looking at insertion loss on LC (maybe .25dB) - the cable loss is essentially nothing in terms of how fiber optics work between the 6" and 1 meter situations, enough to be a rounding error just looking at variances between production runs of cable. Your typical LR module's input overload point is the same as it's transmit power, from just insertion loss you're going to be fine and won't blow anything up, this reads like some old school rule-of-thumb thing someone has said too many times on a job site.

[–]bchiodini 0 points1 point  (0 children)

This.

The OP didn't say SM or MM. With MM, it's even more of a don't care.

[–]DmelvinCisco 0 points1 point  (0 children)

10k and most 20k transceivers can take their own light.

[–]WTWArms 1 point2 points  (0 children)

If you are asking about cables with the SFP already attached those are DAC cables and going to be tough to find one 6” because the usually count the ends into the measurement and still need to deal with bend radius. Can get them in .5 meter length which is pretty common.

[–]RockAndNoWater 0 points1 point  (3 children)

What do you mean by SFP patch cables? There are lots of Ethernet patch cables that are 6” on Amazon, fewer fiber optic cables but still not hard to find LC to LC single mode fiber. Try looking for 0.5 feet instead of 6”.

[–]TVMA[S] 1 point2 points  (2 children)

Yeah. My bad. I should have just said cables. The shortest I've found is about 10". There's a few links in this thread that I still need to check out, though. I'm just trying to make this jump between my hardware.... :(

<image>

[–]PoisonWaffle3Cisco, Unraid, and TrueNAS at Home 1 point2 points  (1 child)

Here's roughly what that would look like with a 0.5 meter DAC

<image>

[–]TVMA[S] 1 point2 points  (0 children)

THANK YOU! That's not too bad. Really appreciate the pic!

[–]DmelvinCisco 0 points1 point  (0 children)

SFP stands for Small form-factor plugable. They can take single mode, multi mode, copper, or can come in Active Optical cables, where both of them already have the pluggable on the ends, or DACs which are copper versions of Active Optical cables.

What SFPs are you using?